@AgentKuga @ramunegaming This is a monthly manga. The next chapter should be released on July 26th and the translation should be up shortly after that.
It may be somewhat spoiler for those who have not read all the chapters available here.
1. Sept - the story of the fall of Hyoka and Tsurara.
2. To demonstrate the development of the history of Hyoka and Isoko, there will be enough flashback ( about extracting Isoko's memory ), in the main manga.
Moreover, there it is likely to be an important moment in the plot for the development of the relationship between the Aya's team and Nana.
@papamiosuckmahdicko I doubt it was axed tbh. It's more likely that Sept was planned to be a short spin-off in general, that ties into the mystery and current events of the the main story.
That way the author didn't have to dedicate a small flashback or mini arc for Hyoka into the main story which would have dragged down the pacing and stretched the main plot even further than necessary. In essence, it's all good mane.